blkio.go: correct help message word spells.
blkio.go: correct help message word spells.

Signed-off-by: Guangming Wang <2dca52765acf93a024077590b100d00c3300ed67@daocloud.io>

crosbymichael/containerd,vdemeester/containerd,estesp/containerd,estesp/containerd,containerd/containerd,dmcgowan/containerd,dmcgowan/containerd,crosbymichael/containerd,mikebrow/containerd,thaJeztah/containerd,vdemeester/containerd,mikebrow/containerd,containerd/containerd,thaJeztah/containerd